Direct Zeeman AAS

Advantages of this technique are (i) Only one light source is used (ii) The technique is not limited to radiation sources operating in the UV region. 

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KuRFiiRST U, Grobecker KH, Stoeppler M (1984) Homogeneity studies in biological reference and control materials with solid sampling and direct Zeeman-AAS. In Schramel P, Bratter P, eds. Trace Element Analytical Chemistry in Medicine and Biology, Vol. 3, pp 591-601. de Gruyter, Berlin. 

The influence of matrix concomitants often cannot be recognised or quantified. Progress in background correction techniques (e.g. direct Zeeman-AAS [218]), furnace techniques, microweighing, and electronic signal processing have gradually made possible the elimination... 

The Zeeman effect arises from the interaction of an external magnetic field ivith the magnetic moment of the emitting (direct Zeeman effect) or absorbing (inverse Zeeman effect) atom, resulting in split emission lines. This phenomenon has made a significant contribution to nonatomic background correction in atomic absorption spectrometry, especially in electrothermal AAS ivhere more serious nonatomic, nonspecific absorptions occur. 

Using pyrolytic graphite tubes, platform atomization and integrated absorbance readings a Zeeman-based instrument provides an acceptable situation for selenium determinations and permits most analyses to be performed against matrix matched calibration graphs. In Table 1 recommended procedures for the direct GF-AAS determination of selenium in body fluids are listed. 

The most significant advantage of inverse Zeeman AAS is that the background is always measured directly at the same wavelength as the atomic absorption of the analyte. This permits accurate correction even when the background is highly structured, but not when non-absorbed lines are present. 

Zeeman-AAS 40-60 suitable for routine, direct measurements in many solid sample types without pretreatment... 

The direct determination of Fe and Se by ET-AAS was proposed without any digestion, that is, just by simple dilution of the milk samples [68, 69, 74]. The elements were determined in bovine milk after dilution of the sample with water-soluble tertiary amines (10 percent). Pyrolytic graphite tubes, Pd as the chemical modifier, and Zeeman background correction were used. The concentration of Fe varied from 0.61 to 1.17 mg l-1 and Se concentrations were in the 17-122 pg l-1 range. 

The parameters gaa, gbb > See 2 aa Xbb -Xcc > and 2Xbb X a Xcc are measured directly and all others are determined from these numbers, the moments of inertia, the molecular structure, and the value of the bulk magnetic susceptibility. The sources of error in these measurements are in frequencies and fields. Of course, for very large Zeeman splittings, the accuracy of the magnetic field becomes critical. The... 

A method for direct Ag determination at ppb levels in blood plasma was developed, based on GF-AAS with Zeeman effect background correction55. Selective preconcentration of several metal ions can be accomplished with poly(chlorotrifluoroethylene). Thus, after SPE of the complexes of Ag(I), Cd(II) or Cu(II) with bismuthiol II (14) at pH 2 and elution with tetrabutylammonium chloride in acetone, the eluate was directly determined by AAS72. Sub ngL-1 concentrations of Ag(I) may be preconcentrated by sorption on finely ground dithizone (12), filtration, dissolution of the dithizone in CHCI3 and end analysis by ET-AAS LOD 1 ngL-1 with no interference by humic acids, fulvic acids or soluble silica73. Ag(I) in river bottom and sea floor was preconcentrated on activated carbon containing dithizone (12), at pH 1.5 a suspension of the carbon was injected into a metal furnace AAS LOD 0.05 pg AgL-1, for 100 mL samples at SNR 359. 

Figure 6.39a explains schematically the appearance of resonances between the fixed frequency cot and the different Zeeman components when the magnetic field B is tuned. The experimental arrangement is illustrated in Fig. 6.39b. The sample is placed inside the laser cavity and the laser output is monitored as a function of the magnetic field. The cell is part of a flow system in which radicals are generated either directly in a microwave discharge or by adding reactants to the discharge close to the laser cavity. A polyethylene membrane beam splitter separates the laser medium from the sample. The beam splitter polarizes the radiation and transitions with either AA/ = 0 or zbl, which can be selected by rotation of the tube about the laser axis. For illustration. Fig. 6.39c shows the laser magnetic resonance (LMR) spectrum of the CH radical with some OH lines overlapping. Concentrations of 2 X 10 molecules/cm could be still detected with reasonable signal-to-noise ratio for the detector time constant of 1 s [6.112,6.113].

Welz et al. [151] investigated in detail the determination of thallium in marine sediment reference materials, a particularly complex topic, because of the volatility of TlCl, and the various spectral interferences that could be observed in the vicinity of the T1 line (refer to Section 8.2.1). The authors had previously investigated this using direct analysis of solid samples and Zeeman-effect BC [142], however they only succeeded in obtaining reliable results when ruthenium was used as permanent modifier, and a solution of ammonium nitrate was pipetted on top of the solid sample as an additional modifier. Method development turned out to be much easier in HR-CS AAS, and the spectral interference due to the sulfur content of the sediments could be completely removed using least-squares BC (refer to Section 8.2.1). 

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